You may want to draw a line under MC whilst your W is active in an A. Why invest your time and energy in this when she is disrespecting your M and you. Why not tell her that you are no longer willing to invest your time and energy in MC, whilst she continues in a R outside of the M.
And you have no need to 'justify' your behaviour towards OM. You may however want to consider a boundary - I do not want to meet OM, I do not want him at our house etc. If he does I will not speak to him, I will ask him to leave etc..
T 13 M 7 Me 48 H 46 SS 15 BD 7.14 PA D final 5.16 (H filed)
We receive & we lose, and must try to achieve gratitude & embrace with whole hearts whatever of life that remains after the losses - Dubus